Morphology and Mechanism of Necrosis

Question 1

What are the morphologic patterns of necrosis?

Answer 1

• Coagulative necrosis
• Liquefactive necrosis
• Caseous necrosis
• Ganrenous necrosis
• Fat necrosis

Question 2

What is Coagulative Necrosis?

Answer 2

• Cell and tissue death de to loss of enerrgy
  
  • Most often due to hypoxia
• Basic mophology of teh tissue and cells are retained but have a “ghost-like” apearance
  
  • Cell proteins become denatured

Question 3

What causes coagultive necrosis?

Answer 3

• Loss of energy
  
  • most often due to hypoxia
• Oxygen metabolites
  
  • highly reactive free activities
• Toxin
  
  • Direct acting toxins
  • Indirect acting toxins that must be biotransformed before they damage cels

Question 4

What is the morphology of Necrosis

Answer 4

• Gross:
  
  • Tisse is pale and dr
    
    • With infrcts, tissue can be dark red to to blood backflow
  • Frequenty surrounded by a zone of inflammation
• Histologic:
  
  • Basic cell outlines are retained
  • Nucleai are:
    
    • shrunken (pyknotic)
    • Fragmented (karyorrhexis) or
    • absent (karyolysis)
  • Eventually there is lysis of necroti tissue

Question 5

What is Liquefactive Necrosis?

Answer 5

• Cell and tissue death associated with liquefaction in response to neutrophl enzymes
• Tissue morphology is replaced by liquified debris (Pus)
  
  • An abscess is liquifactive necrosis/suppurative inflammation

Question 6

What causes liquefactve necrosis

Answer 6

• pyogenic bacterial infection
• Hypoxia in the nervous system

Question 7

What is the morphology of liquifactive necrosis?

Answer 7

• Gross:
  
  • Focal pus accumulation (abscess)
    
    • necrotic neutropils and ebris
  • Inspissation of pus can give the tissue a more caseous (dry and crumbly) look
• Histological:
  
  • Neutrophils
  • Liquefaction of tissue in respons to neutrophil enzymes
  • Outer fibrous casule in mature lesions

Question 8

What is caseous necrosis

Answer 8

• type of coagulative necrosis where teh necrotic tissue is surrounded by a hronic inflammator response
  
  • Older lesions contain poorly degradable bacterial lipids
  • liiquifaction can occur if there are neutrophils present
• Usually a component of granuloma formation

Question 9

What causes caseous necrosis?

Answer 9

• Classically described form of necrosis associated with tuberculosis (Mycobacterium)
• Bacteria with dense, wazy cell walls
• Fungi and higher organisms
• Foreign bodies

Question 10

What is the morphology of caseous necrosis?

Answer 10

• Gross:
  
  • Granular, friable mass (cottage cheese-like)
  • Fibrous capsule
• Histologic:
  
  • Central core of cell debirs
  • Surrounding zone of inflammation
    
    • Lymphocyes and plasma cells
    • Macrophages
  • Outer fibrous capsule in mature lesions

Question 11

What is gangrenous necrosis?

Answer 11

• A subset of coagulative and liquifactive necrosis that has a distictive morphology and locattion
  
  • 3 morphologic types of gangrene:
    
    • Dry
    • Wet
    • Gas

Question 12

What is dry gagrene?

Answer 12

• Affects the distal extremeties (limbs/digits, ears, tail)
• Coagulation necrosis due to ischemia/infarction
• Dry, brown to black, shriveled tissue
  
  • Due to infarction and mummification
• Examples inclue ergot alkaloids (fescue foot) and frostbite
• In humans this occurs manly due to peripheral vascular diseae, often associated with arteriosclerosis or diabetes mellitus

Question 13

What is wet gangrene?

Answer 13

• Most common in dependent portion of organs, such as the lunge or mammary gland
• Liquefactive necrosis with saprophyticbacterial infection
• Soft, red-brown to black tissue
  
  • Due to liquifaction of tissue by neutrophils
• Animals can often become septic

Question 14

What is gas gangrene?

Answer 14

• Variant of Wet gangrene, where bacteria are gas producers (Ex: clostridia)
• Exudative, brown to black tissue containing gas
  
  • Due to proliferation of gas-producing bacteria

Question 15

What are the causes of gangrenous necrosis?

Answer 15

• Ischemia with desiccation
• saprophytic bacteria

Question 16

What is the morphology of gangrenous necrosis

Answer 16

• Histologic:
  
  • Dry: coagulation necrosis with desiccation
  • Wet: Coagulation necrosis progressing to liquefaction of tissue
  • Gas: Liquefaction with serohemorrhagic fluid and gas bubbles

Question 17

What is Fat necrosis?

Answer 17

• Process that occus in fat due to the destruction of adipocytes by lipase
  
  • most commonly occurs in association with pancreatitis
• Unlike other paterns of necrosis, which can occur in any tissue, this process is specific for fat.

Question 18

What causes fat necrosis?

Answer 18

• Enzymatic destruction due to pancreatitis
• Traumatic crushing of fat
• Idiopathic
  
  • fat necrosis of abdominal fat in cattle

Question 19

What is the morphology of Fat necrosis?

Answer 19

• Gross:
  
  • tissue is white, firm and chalky
• Histologic:
  
  • adipocytes are eosinophilic but retain normal architecture
  • Basophilic areas may be present due to calcium binding (saponification